The present invention relates to a method of manufacturing a semiconductor device having a structure wherein active regions are stacked, such as a transistor or the like and which is known as a three-dimensional IC.
In recent years, many technologies and structures have been proposed with respect to a technology for forming a stacked single crystalline semiconductor layer as the most fundamental and important technology in the manufacture of the so-called three-dimensional IC, particularly with regard to the SOI (Semiconductor On Insulator) structure. For example, there are the zone melting method employing a carbon strip heater or the like, and a method whereby the recrystallization is performed by irradiating with laser or electron beam, and the like. In the heating method employing a carbon heater or the like, the whole substrate is heated to over 1000.degree. C. from a long time. Therefore, this method is suitable for obtaining only the SOI structure. However, it is difficult to apply such a method to the case of manufacturing a three-dimensional IC in which active layers including devices are stacked because the devices which have already been formed in the lower layer are thermally damaged and eventually broken.
Therefore, in order to obtain a single crystalline layer in the stacked structure, a recrystallizing method employing irradiation with a laser or electron beam to effect local heating of only the surface layer is highlighted as an effective means. As conventional examples, most such methods adopt the SOI structure and in such a case, a flat uniform insulating film is disposed under the layer to be recrystallized, so that a good crystallized layer can be easily obtained. In addition, in case of the SOI, in order to obtain a preferable crystallized semiconductor layer, as a method of obtaining a desirable temperature distribution at the time of solidification, it is desirable to provide a layer serving as a heat sink under the lower layer of the insulating film. For example, when the SOI is constituted by forming an insulative material on a silicon substrate, this silicon substrate functions as a heat sink.
On the other hand, a few so-called three-dimensional devices in which devices of two or more layers are stacked have been proposed so far. However, most of them are constituted by merely stacking a transistor through an insulating film, so that the crystalline property and the like of the semiconductor layer of the upper layer in which a device should be formed are not good and the electrical characteristics of the device are not good.
Namely, when the crystalline semiconductor layer of the second layer in which a device should be formed is melted and recrystallized due to the irradiation of a laser or electron beam, the temperature distribution is not controlled because of the rough surface shape due to the concave and convex portions of the device formed in the lower layer and because of the irregularity of wiring material and the like, or due to other reasons. Thus, nuclei will have been formed and have grown at random due to the influence of the under layer. Consequently, the recrystallized layer of the semiconductor will have become an assembly of fine crystal grains containing a number of crystal grain boundaries and defects and the like, causing degradation of electrical characteristics. Further, in case of forming the recrystallized semiconductor layer of the second layer, there are some cases where a device in the lower layer which has already been formed is thermally damaged by the beam energy of the laser or the like and its characteristics deteriorate. As mentioned above, in the manufacture of a stacked three-dimensional IC, it is extremely difficult at present to obtain single-crystallized semiconductor layers of the second and subsequent layers without causing the device in the lower layer to be damaged.